Parkes observations for project P1030 semester 2019OCTS_01

The popular carousel model used to explain subpulse drifting in pulsars is criticised on both physical and empirical grounds. In the absence of relativistic effects (aberration and retardation, AR), it predicts that subpulses undergo only amplitude modulation (i.e. no phase modulation) as a function of frequency. A recently advanced model incorporates AR effects and predicts a subpulse phase shift whose magnitude depends crucially on the assumption of the carousel model that the subpulses originate in discrete structures (sparks) that exist very close to the pulsar's surface. We propose to test this theory by measuring the subpulse phase shift of three pulsars which all exhibit different kinds of frequency evolution of their profiles. This requires both high time resolution of single-pulse data and a wide frequency band, as uniquely offered by the UWL. Our primary target (B1857-26) satisfies all of the conditions required by the proposed test. Two other targets (B1944+17 and B2003-08) also offer unique opportunities to study frequency-dependent subpulse phase shifting in the presence of rare phenomena relating to profile evolution and subpulse drifting. We anticipate that the study of these three pulsars will enable us to conclusively determine whether the carousel model and AR effects are able to account for the frequency-dependent behaviour of individual subpulses.

当前用于解释脉冲星亚脉冲漂移现象的旋转木马模型（carousel model）在物理与实证层面均受到质疑。在忽略相对论效应（光行差与延迟，aberration and retardation, AR）的前提下，该模型预测亚脉冲仅会随频率变化发生调幅，即无调相现象。近期提出的新模型纳入了AR效应，并预测亚脉冲会产生相移，其相移幅度高度依赖于旋转木马模型的核心假设：亚脉冲起源于极贴近脉冲星表面的离散结构（即“火花”，sparks）。我们提出通过测量三颗脉冲星的亚脉冲相移来检验该理论，这三颗脉冲星的辐射轮廓均呈现出不同类型的频率演化特征。该研究要求单脉冲数据具备高时间分辨率，同时需要宽频带观测条件，而UWL恰好可提供此类独特的观测支持。我们的首要观测目标B1857-26完全满足本次检验所需的全部条件。另外两颗目标天体B1944+17与B2003-08，则为研究存在辐射轮廓演化与亚脉冲漂移相关稀有现象时的频率依赖亚脉冲相移提供了独特契机。我们预期，对这三颗脉冲星的研究将能够明确判定：旋转木马模型与AR效应是否可以解释单个亚脉冲的频率依赖行为。